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  <script>
    // 编写一个函数，接受一个数组作为参数，并返回数组中所有偶数的和
    let arr = [1,2,3,4,5,6,7,8,]
    let sum = 0
    function and(a){
      for(let i = 0; i < a.length+1; i++) {
        if(a[i] % 2 === 0 ){
          sum +=a[i]
        }
      }
      return sum    
    }
    console.log(and(arr));
  </script>
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